Separation of aromatic/aliphatic mixtures by pervaporation using ortho-functionalized polyimide membranes

The performance of a series of soluble aromatic polyimides for the separation of benzene/n-heptane and toluene/n-heptane mixtures by pervaporation is reported. Homo- and random copolyimides were synthesized by a two-step polycondensation of three aromatic dianhydrides (6FDA, ODPA, BTDA) and five aromatic diamines (APAF, HAB, 3MPD, 4MPD, and FDA). Pervaporation experiments were performed at 80°C with feed streams containing 40 wt% aromatics. All polymers were selective towards the aromatic hydrocarbon, whose permeability could be changed by 4 orders of magnitude depending upon the chemical structure of the diamine. Pure-liquid sorption experiments at 25°C revealed that these large changes in hydrocarbon permeability were mainly caused by changes in the diffusion coefficient. The performance of the synthesized materials was compared with previous results reported for other polymers, as well as with the performance of Matrimid®, a commercial polyimide.